Method and furnace for the vapor phase deposition of components onto semiconductor substrates with a variable main flow direction of the process gas

ABSTRACT

The invention relates to a method and to a furnace for the vapor phase deposition of components onto semiconductor substrates. The main flow direction of the process gases can be varied or reversed in the course of the method. This prevents temperature and concentration inhomogeneities of the process gas within the furnace, and the components to be uniformly deposited onto the semiconductor substrates.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a method and a furnace for the vaporphase deposition of components onto semiconductor substrates.

[0003] As the computer power and the storage capacity of microchips havebeen continually increasing, the integration density of the electroniccomponents, such as transistors or capacitors, has continuallyincreased. What is referred to as Moore's law, which describes adoubling of the integration density in a period of 18 months, has thusheld true for more than 30 years. In the future, the industry willattempt to increase the performance of microchips and also specialcomponents such, as e.g. video chips, in the context of Moore's law sothat the electronic components must be miniaturized further.

[0004] A higher degree of integration is essentially achieved by furtherreducing the size of the functional elements. This concurrently leads toan increase in the operating speed of the microchip. In parallel with arising integration density, there is also an increase in the averagewafer diameter and thus in the demands on the homogeneity of the wafersurface or the layers deposited thereon. Therefore, the realization ofsubmicron structures is at the present time one of the most importanttasks for the further development of microelectronics. This gives riseto more stringent requirements made of the entire technology forfabricating microelectronic components. The individual technologicalsteps must in part be utilized right up to their fundamental limits andnew methods must be developed and introduced into industrial production.

[0005] One typical production step in the fabrication of microchips isthe deposition of a layer made of a specific layer material on a wafer.The layer may be modified, if appropriate, in terms of its chemicaland/or physical properties in a further production step. The depositedand, if appropriate, modified layer may subsequently be patterned byselectively removing specific sections of the layer. The layer may beproduced by oxidizing or nitriding the wafer in a suitable atmosphere,for example, in order to obtain a layer made of silicon oxide or siliconnitride. Layers of these and other materials are preferably produced bymethods utilizing relatively low temperatures. One example of such amethod is chemical deposition from the vapor phase (chemical vapordeposition, CVD), which is usually carried out at temperatures of a fewhundred degrees Celsius and within a wide pressure spectrum. In CVDmethods, a substrate in a CVD process space is exposed to a flowincluding one or more gaseous components. The process gases are, by wayof example, gaseous chemical precursor compounds of the layer materialor inert carrier gases which transport the precursor compounds in solidand liquid form. The layer material is produced from the precursorcompounds photolytically, thermally and/or in plasma-enhanced fashion inthe CVD process space and/or above the substrate surface. The layermaterial is deposited on the substrate surface and forms a layer.

[0006] A high integration density as demanded particularly in the caseof electronic components, such as processors and semiconductor memorydevices, presupposes very small layer thicknesses and small dimensionsfor structures in the layer. Layer thicknesses of a few nanometers andstructure dimensions of a few tens of nanometers have become customaryin the meantime.

[0007] The continual miniaturization increases the demands on the layerquality determined by the defect density, roughness and homogeneity ofthe layer. In this case, the roughness describes a deviation of asurface of a layer from an ideally planar surface. The defect density isa measure of the number and the size of impurities or structural defectsin the layer.

[0008] In this case, impurities are inclusions made of a differentmaterial than the layer material.

[0009] Structural defects may be, by way of example, voids or, in thecase of crystallizing layer materials, lattice defects. Homogeneityrelates to the physical and chemical uniformity of the layer. Customarymethods for fabricating layers having a layer thickness of less than 1μm on a substrate are epitaxial methods, physical vapor phase deposition(physical vapor deposition, PVD methods) and chemical vapor phasedeposition (chemical vapor deposition, CVD methods).

[0010] The layers are deposited in single-wafer installations or inmultiwafer installations. In multiwafer installations, a plurality ofwafers are stacked one above the other at a short distance in a suitablerack. The rack, referred to as a “boat”, charged with a plurality ofwafers is then introduced into the process space of a furnace. Theprocess gas containing the components to be deposited is introduced forexample at the underside of the process space and then rises laterallypast the wafers stacked one above the other and upward along this flowdirection. This flow direction along which the principal convectionmaterial transport takes place is referred to as the main flowdirection. The process gas is discharged at the top side of the processspace. For this purpose, the process gas may either be passed outthrough a discharge line at the upper side of the furnace or it may bedeflected and passed downward on the outside of the process space inorder then to be pumped away at the underside of the furnace. Thecomponents contained in the process gas diffuse out of the main flowflowing laterally upward past the wafer stack into the interspacebetween two wafers arranged one above the other in order then to reachthe wafer surface and subsequently be deposited there. The mass transferis principally effected by diffusion, but other phenomena such asconvection and thermodiffusion (Soret effect) are involved. In thiscase, the diffusion flow of the components out of the main flow into thespace between the wafers is determined by the concentration gradient ofthe components in the main flow of the process gas. While the processgas rises from the bottom upward, it is thus continuously depleted ofcomponents. The consequential products thereof are deposited on thesurface of the wafers, with the result that a concentration gradient isestablished along the main flow direction. Since the quantity of thecomponent that is transported out of the main gas flow between thewafers depends on the set concentration gradient of the component in themain gas flow, it is possible for a larger quantity of the component topass into the interspace between two wafers arranged one above the otherin the lower region of the process space, in which the main gas flowstill has a high concentration of the component, than in the upperregion of the process space in which the main gas flow is largelydepleted of the component. The consequence of this is that the thicknessof the deposited layer is larger on wafers arranged in the lower regionof the process space than in the case of wafers arranged in the upperregion of the process space. Such inhomogeneities are not infrequentduring nitride deposition. An analogous effect is observed when dopingthe silicon wafers. A high doping is effected in the lower region of theprocess space into which fresh dopant is continually fed, while asignificantly lower doping is effected in the upper regions.

[0011] The inhomogeneities produced in this way within the process spacelead to a nonuniform distribution of the material parameters of thetreated semiconductor substrates within a batch and, associated withthis, to different electronic properties of the same component ondifferent wafers of a batch. However, in microelectronics, inparticular, extremely stringent requirements are made of the stabilityand the reproducibility of the fabrication steps of the electroniccomponents.

[0012] Therefore, efforts have been made to combat the different ratesof deposition of the components on wafers of a batch.

[0013] Thus, it has been proposed to provide injectors in the processspace along the main flow direction. These injectors would enabledopants or other components, which are to be deposited on the wafer, tobe fed into the process space. In this way, it is possible to replacethe quantity of the component that has been removed from the process gasand deposited on the wafer. This means that a depletion of the componentin the process gas is counteracted and the change of the concentrationgradient in the process gas along the main flow direction can besuppressed. However, this solution is technically very complicatedsince, on the one hand, it is necessary to incorporate injectors intothe process space and, on the other hand, the quantity of component fedto the process space by the injectors has to be regulated such that onlythe consumed quantity of the component is replaced in each case.However, injectors are highly susceptible to functional failures, suchas those that occur for example, due to mechanical fracture defects.

[0014] A further possibility that is afforded is to use smaller batchsizes in order to minimize differences between the first and last wafersof a batch. However, the lower turnover per fabrication cycle means thatit is necessary to expend a higher outlay with regard to costs, as aresult of which the economy of the method decreases.

[0015] Furthermore, in order to balance the layer thicknesses obtained,it is possible to provide a temperature gradient within the processspace. The deposition rate which is increased at a higher temperaturemakes it possible to counteract the depletion of the component to bedeposited in the main gas flow. Temperature differences of severaldegrees are not infrequent, as during nitride deposition, in particular.With this method, although it is possible to achieve uniform layerthicknesses within a batch, the wafers of a batch nonetheless experiencea different thermal budget. As a result, in later process steps,differences may occur in the processing of the wafers or, in thefinished product, differences may occur in the electronic parametersbetween chips from different wafers.

[0016] In single-wafer installations, nonuniformities of temperature andconcentration profiles can be compensated for by rotating the waferabout its axis. This method is offered by most manufacturers nowadays.This method is unfavorable for multiwafer installations since a rotationof the wafers or of the boat can be realized technically only withdifficulty and, in multiwafer installations, the main flow direction ofthe process gas generally runs parallel to the normal to the wafer areaand not parallel to the wafer surface, which is the case in single-waferinstallations. Therefore, a concentration gradient along the main flowdirection cannot be compensated for by rotating the boat about itslongitudinal axis. This means that the boat rotation essentially onlyhas a positive effect on the uniformity within a wafer, but thehomogeneity of the individual wafers among one another is barelyinfluenced.

[0017] In this case, the aspect of the uniformity of the wafers amongone another becomes all the more critical, the smaller the feature sizesbecome. If the critical feature size is to be reduced further, theregularity with which layers are deposited within a batch must beincreased further.

SUMMARY OF THE INVENTION

[0018] It is accordingly an object of the invention to provide a furnaceand a method for vapor phase depositing components on a semiconductorsubstrate, which overcome the above-mentioned disadvantages of the priorart apparatus and methods of this general type.

[0019] In particular, it is an object of the invention to provide amethod for vapor phase depositing components on a semiconductorsubstrate in which, even in the case of relatively large batch sizes,only slight fluctuations in the layer properties between two wafers areobserved or in which fluctuations in the layer thickness of a layerdeposited on a semiconductor substrate can be reduced.

[0020] With the foregoing and other objects in view there is provided,in accordance with the invention, a method for vapor phase deposition.The method includes: vapor phase depositing components contained in aprocess gas flowing along a main flow direction onto at least onesemiconductor substrate situated in a process space; and during the stepof vapor phase depositing, changing the main flow direction at leastonce.

[0021] In the method, the semiconductor substrates are first arranged ina customary manner in the process space. If a plurality of semiconductorsubstrates are situated in the process space, they are generallyarranged (stacked) one above the other at a short distance. The processgases containing the components that are to be deposited on thesemiconductor substrate are subsequently introduced into the processspace. For this purpose, the process space includes at least one feedline that can be opened or closed off e.g. by a supply valve and throughwhich the process gas is supplied to the process space, and also atleast one discharge line through which the process gas is passed out ofthe process space by being pumped away, for example. A main flowdirection along which the process gas flows through the process space isestablished between the feed line and the corresponding discharge line.As described above, a first concentration gradient is established in theprocess space for the components supplied. The concentration gradientleads to fluctuations in the layer thickness between individualsemiconductor substrates of a batch or, in single-wafer installations,on the surface of the semiconductor substrate. If the main flowdirection is then changed, a second concentration gradient isestablished, which differs from the first concentration gradient. Thefluctuations that are observed within a batch between individualsemiconductor substrates or, in single-wafer installations, on thesurface of the wafer also change as a consequence. The changeover of themain flow direction is effected, if possible, such that the fluctuationsin the properties of the deposited layer which are established betweenthe individual semiconductor substrates of a batch in a multiwaferinstallation or on the surface of the semiconductor substrate in asingle-wafer installation are largely compensated for.

[0022] Thus, by changing the main flow direction once or a number oftimes, it is possible to compensate for concentration gradients that areestablished for the components in the process space. As a result, it isalso possible to avoid different layer thicknesses on semiconductorsubstrates of a batch, so that it is possible to achieve a significantlymore uniform quality of the processed semiconductor substrates.

[0023] The method improves the uniformity of the treated semiconductorsubstrates, for example, with regard to the thickness of the depositedlayer or a doping. It is not necessary to provide a temperature gradientin the process space. The temperature can be kept constant or can bevaried uniformly in the entire process space. The semiconductorsubstrates of a batch therefore all experience the same thermal budget,i.e. they are heated to the same temperature for the same period oftime. As a result, the reproducibility of the electronic properties ofthe microelectronic components produced is increased and the yield offunctional circuits is increased.

[0024] An essential advantage of the method is the possibility ofincreasing the batch size further. The variable main flow directionsignificantly reduces the problem which concerns local concentrationdepletion and occurs particularly with relatively larger batch sizes. Itis thus possible to use significantly larger batch sizes and thus tofabricate more components than hitherto within a production cycle. Theeconomy of the method is significantly improved as a result.

[0025] The method is inherently independent of the size of the processedsemiconductor substrates. Thus, wafers having a relatively largediameter, e.g. having a size of 300 mm or more, can also be processedwithout any problems. It goes without saying, however, that the methodcan also be used for processing smaller wafers.

[0026] Since concentration gradients in the process space are largelycompensated for in the course of the method, it is sufficient if dopantsfor controlling the electronic properties of the semiconductorsubstrates are introduced into the process space as a process gas atonly one location. Therefore, it is not necessary to provide lateralinjection nozzles (injectors) along the main flow direction in theprocess space in order to compensate for a depletion of dopant in theprocess gas. The apparatuses suitable for carrying out the method cantherefore be embodied in a structurally simple manner and are thereforeinsensitive to technical disturbances.

[0027] Of course, installations equipped with injectors may likewise beoperated using the method, and use of the injectors can provide for anadditional increase in the homogeneity.

[0028] The method thus improves the uniformity within a wafer batch.This relates both to the layer thickness and to the doping and thethermal budget. As a result, the reproducibility of the electronicproperties of the electronic components fabricated from thesemiconductor substrates is improved and, consequently, the yield of thecircuits thereby fabricated is increased. This results in an increasedyield of functional components and an associated increase in theproductivity of the method.

[0029] In a preferred embodiment of the method, the main flow directionis reversed. A reversal of the main flow direction corresponds to amaximum change in the main flow direction. A maximum change in the flowswithin the furnace and thus an extensive compensation of concentrationand temperature gradients take place in this case. As already describedabove, in multilayer installations, the semiconductor substrates arearranged in the process space in a manner stacked one above another at ashort distance, and the process gas flows laterally past the stackforming a main flow direction. For this purpose, the process gas may beintroduced into the process space e.g. at the underside. After aspecific period of time, the main flow direction is reversed, i.e. theprocess gas is then introduced at the top side—opposite to theunderside—of the process space. The main flow direction thereforechanges by 180°. In single-wafer installations, the process gas flowsparallel to the wafer surface. In this case, too, the main flowdirection is reversed, that is to say rotated through 180°, after aspecific period of time in order to compensate for concentration andtemperature gradients. In single-wafer installations, it may beadvantageous to change the main flow direction in smaller steps, e.g. by90° in each case, in order to achieve an optimum compensation of thetemperature and concentration gradients.

[0030] Therefore, it is advantageous if the main flow direction isoriented parallel to an axis of symmetry of the semiconductorsubstrates. In the event of a change in the main flow direction,concentration gradients are compensated for in a symmetrical manneralong the axis of symmetry of the substrates. The homogeneity of thecoated semiconductor substrates can then be significantly improved.

[0031] The axis of symmetry is preferably a rotation axis or a rotarymirror axis. These axes of symmetry have a particularly high degree ofsymmetry in comparison with other axes of symmetry, so that aparticularly effective compensation of the concentration gradients isachieved when the main flow direction is oriented parallel to such anaxis of symmetry. In multiwafer installations, the rotation axis runsperpendicular to the surface of the semiconductor substrate in thecenter of the stack. Therefore, as already described, the process gasflows laterally past the semiconductor stack along the main flowdirection. In single-wafer installations, the rotary mirror axis runsalong the wafer surface through the midpoint of the surface of thesemiconductor substrate. The process gas therefore flows parallel to thewafer surface along the main flow direction across the semiconductorsubstrate.

[0032] In a preferred embodiment of the method, the process gas is atleast partially removed from the process space before changing the mainflow direction. The process gas introduced into the process spacedirectly before changing the main flow direction no longer traverses theentire path through the process space, but rather experiences a flowreversal. If one takes a specific volume of the process gas flow whichwas introduced into the process space shortly before the flow reversal,the volume, up to the flow reversal, passes only as far as one of thelower semiconductor substrates of the stack in order then to bedischarged from the process space in the opposite direction. Thesemiconductor substrates at the outer ends of the stack thereforeexperience an additionally intensified layer thickness growth. Theeffect may become apparent particularly when the main flow direction ischanged repeatedly. Through skilful implementation of the method, thiseffect can be utilized to compensate for a reduced layer thicknessgrowth at the ends of the wafer stack, caused by the low concentrationof the components in the process gas, before this leaves the processspace during the customary deposition. In order to avoid additionalinhomogeneities, however, it is more favorable for process gas that isstill present in the process space to be removed before the change inthe main flow direction. As a result, fresh process gas can beintroduced into the process space, which then flows through the processspace over its entire extent. The desired concentration or temperaturegradient then forms directly.

[0033] The removal of the process gas from the process space may beeffected by reducing the supply of process gas into the process spaceand/or by extracting process gas from the process space and/or byflushing the process space with an inert gas (e.g. noble gas ornitrogen). In the case of the embodiment mentioned last, pressure surgesin the reaction chamber are avoided.

[0034] The composition of the process gas supplied usually remainsunchanged during the deposition of a layer or the introduction of adoping. It may be advantageous for specific requirements, however, ifthe components have a different composition and/or concentration afterthe change in the main flow direction. The flexibility of the method isthereby increased and it is possible, for example by using differentdopant concentrations, to produce specific doping profiles in thesemiconductor substrates and thereby to adapt electronic properties in atargeted manner.

[0035] Furthermore, by changing the composition of the process gas, itis possible, by way of example, also to realize layers including aplurality of different layers or particular defect structures, e.g. bychanging the dopant.

[0036] According to one embodiment of the method, layers are fabricated,and the components contained in the process gas react chemically withthe material of the semiconductor substrates. A chemical reactionbetween the components to be deposited and the semiconductor substratesliberates significantly higher quantities of energy than physicaladsorption. The stability thereby achieved in the deposition layerproduced is accordingly significantly higher, as a result of whichservice life and resistance to external influences such as mechanicaland thermal loads or behavior toward moisture and chemicals can beoptimized. Examples of such layers are layers made of silicon dioxide orsilicon nitride. However, the method is also suitable for thefabrication of layers in which the components contained in the processgas all form the starting materials for the layer. In this case, thecomponent may be deposited directly as the material of the layer (PVD;“Physical Vapor Deposition”) or the material of the layer may be formedin a chemical reaction (CVD; “Chemical Vapor Deposition”).

[0037] The vapor phase deposition can take place at atmosphericpressure, subatmospheric pressure, and in the near-vacuum range,subatmospheric pressure is preferred.

[0038] In a preferred embodiment of the method, the change in the mainflow direction is effected in accordance with a variable time pattern.As a result, by way of example, it is possible to change the main flowdirection with a higher frequency at the beginning of the vapor phasedeposition in order first to obtain a starter layer that is as uniformas possible on all the semiconductor substrates. In a later stage of themethod, when a constant deposition rate has been established for theindividual semiconductor substrates, a lower frequency of the change inthe main flow direction with longer interval ranges may then also besufficient. In the case of depositions wherein the deposition rateremains essentially constant during the entire deposition, one change ofdirection is enough.

[0039] In a further embodiment of the method, an online detection of thequantity and/or the distribution of the components deposited onto thesemiconductor substrates is effected during the method. As a result, theinstantaneous deposition results with regard to the layer thickness andthe quality are obtained directly. In the event of disturbancesoccurring or incomplete deposition, corresponding measures andcorrections can be initiated immediately, so that it is possible tofabricate layers with high quality reproducibly.

[0040] An essential feature of the method is the change in the main flowdirection in the process space. Therefore, specially configured furnacesare required to carry out the method. Therefore, the invention alsorelates to a furnace for the vapor phase deposition of componentscontained in a process gas onto one or more semiconductor substrates.

[0041] With the foregoing and other objects in view there is provided,in accordance with the invention, a furnace for vapor phase depositingcomponents contained in a process gas onto at least one semiconductorsubstrate. The furnace includes: a process space for receiving thesemiconductor substrate; a first feed/discharge line connected to theprocess space; a second feed/discharge line connected to the processspace; a device for producing a process gas flow, the device forproducing the process gas flow connected to the first feed/dischargeline and/or the second feed/discharge line; a heating device; and aregulating unit for regulating a magnitude and a flow direction of theprocess gas flow.

[0042] This furnace makes it possible to achieve a homogeneousdeposition of components on semiconductor substrates, so that a uniformcoating of the semiconductor substrates with regard to layer thicknessand layer quality is obtained even with extensive batch sizes. Thefurnace may be configured both as a single-wafer installation and as amultiwafer installation.

[0043] Since the electronic properties depend significantly on thematerial properties, the electronic quality of the microelectroniccircuits produced from these semiconductor substrates is significantlyimproved. Therefore, the furnace makes it possible to fabricatemicroelectronic components with reduced dimensions.

[0044] The furnace differs from the furnaces used hitherto essentiallyby virtue of providing an apparatus that can vary or reverse the flow inthe process space of the furnace. As already explained in connectionwith the method, a process gas containing the components to be depositedflows through the process space. The process gas is depleted because ofthe deposition of the components, so that a concentration gradient isestablished in the process space for the components along a main flowdirection. If the flow conditions are varied by varying the flowdirection, the concentration gradient is also varied. As a result of thesuperposition of the concentration gradients, it is possible in total toachieve a more uniform deposition of layers, in particular a uniformlayer thickness within a batch.

[0045] First and second feed and discharge lines may inherently beconfigured in any desired manner. Thus, the first and secondfeed/discharge lines may be configured in each case as two lines openinginto the process space. In each case, one of the lines acts as the feedline and the other as the discharge line. In this case, then, at leastfour lines open into the process space. However, feed and dischargelines may also be connected to the process space via a common access, sothat only two lines open into the process space. It is also possible,however, for the feed and discharge lines to also be configured in theform of injectors as a plurality of feed and discharge lines in order,by way of example, to obtain a uniform flow of the process gas in theprocess space. In order to produce a flow in the process space,provision is correspondingly made of a device for producing a processgas flow, which is connected to the first and/or second feed/dischargeline. Pumps are generally used for this, as are also customary in thefurnaces used hitherto. The flow can be produced, for example, byforcing the process gas into the process space or by pumping the processgas out of the process space.

[0046] In order to achieve a flow reversal of the process gas, devicesfor regulating the magnitude and the flow direction of the process gasflow is provided. These may be valves, for example, for opening orclosing the first and second feed/discharge lines. It is also possible,however, to influence the main flow direction using the device forproducing a process gas flow, e.g. by correspondingly regulating theconveying capacity of a pump. The device for regulating the magnitudeand the flow direction may be controlled in a computer-aided manner, forexample.

[0047] Preferably, the first and second feed/discharge line are arrangedat opposite sides of the process space. A reversal through 180° is theneffected in the event of a change in the flow. This is particularlyadvantageous in multiwafer installations, since the concentrationgradients are particularly pronounced here. First and secondfeed/discharge lines are advantageously provided at the underside andtop side of the process space, that is to say in the lengthening of aboat that is arranged in the process space and is charged with wafers.

[0048] In accordance with a further embodiment, an interval regulatingunit is provided, for changing the direction of the process gas flow atintervals according to a variable time pattern. As a result, inaccordance with the course of the method, it is possible to realizesuitable time windows for the individual deposition intervals. Asalready explained for the method, it may be advantageous at thebeginning of a deposition cycle to provide a high frequency for thechange in the main flow direction in order first to produce a thinstarter layer uniformly on all the semiconductor substrates. Thisstarter layer then acts as a seed layer for the subsequent deposition ofthe layer. Once a uniform layer growth has been initiated on the entiresurface of the individual semiconductor substrates, it is also possibleto use a lower frequency for changing the main flow direction. In thisway, it is also possible to produce thicker layers with thicknesses ofseveral micrometers, in which only slight fluctuations in the layerthickness within a batch are observed.

[0049] In order to be able to precisely control the growth of the layer,in accordance with a further embodiment of the furnace, there isprovided, a measuring unit for detecting the quantity and/ordistribution of the components deposited onto the semiconductorsubstrates. This measuring unit can be connected to the device forproducing a process gas flow in order to control the process gas flow orthe concentration of the components supplied.

[0050] In accordance with a preferred embodiment of the furnace, thereis provided, a control unit connected to the measuring unit and servingfor the online control of the device for producing a process gas flow.On the basis of the data determined by the measuring unit, it is thenpossible automatically to intervene in the deposition process and thusto influence the growth of the layer.

[0051] Other features which are considered as characteristic for theinvention are set forth in the appended claims.

[0052] Although the invention is illustrated and described herein asembodied in a method and furnace for the vapor phase deposition ofcomponents onto semiconductor substrates with a variable main flowdirection of the process gas, it is nevertheless not intended to belimited to the details shown, since various modifications and structuralchanges may be made therein without departing from the spirit of theinvention and within the scope and range of equivalents of the claims.

[0053] The construction and method of operation of the invention,however, together with additional objects and advantages thereof will bebest understood from the following description of specific embodimentswhen read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0054]FIG. 1 is a diagrammatic illustration of a furnace;

[0055] FIGS. 2A-2D are diagrammatic illustrations of a furnace;

[0056]FIG. 3 is a graph of the layer thickness distribution in a batchobtained when carrying out the method; and

[0057]FIG. 4 is a graph of the layer thickness distribution in a batchobtained when carrying out a prior art method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] Referring now to the figures of the drawing in detail and first,particularly, to FIG. 1 thereof, there is shown a diagrammaticillustration of a longitudinal section through a furnace 1. A processspace 3 delimited by a partition 2 is arranged within the furnace 1. Byway of example, a heating device 16 may be arranged behind the partition2. Situated in the process space 3 is a boat 4, which includes a rack inwhich wafers are arranged one above the other at a short distance. Forthe sake of clarity, the rack and the wafers are not illustrated indetail. Dummy wafers 5 are arranged in the outer sections of the boat 4,that is to say at the top side and underside thereof, which dummy wafers5 on both sides delimit the stack of the wafers 6 to be processed. Thedummy wafers 5 serve for producing uniform flow conditions in the regionof the wafers 6 to be processed. A first feed/discharge line 7 isprovided at the underside of the process space 3, through which line 7process gas can be supplied to the process space 3 and process gas canbe conducted out of the process space 3. In order to be able toinfluence the flow of the process gas, a valve 8 is provided. Theopening and closing of the valve 8 is controlled by a regulating unit 9,which is connected to the valve 8 via control lines 10.

[0059] Finally, a pump 11 is provided for producing a gas flow. The pump11 can either convey process gas into the process space 3 or extractprocess gas from the latter, via the first feed/discharge line 7. Theoperating state of the pump 11 is likewise controlled by the regulatingunit 9, which is connected to the pump 11 by corresponding control lines10. A second feed/discharge line 12 is arranged at the side of theprocess space 3 that is opposite to the first feed/discharge line 7. Thegas flow through the second feed/discharge line 12 can be regulated byvalve 13, which is controlled by the regulating unit 9. The regulatingunit 9 is connected to the valve 13 via control line 10. The pump 14 cansupply process gas to the process space 3 or discharge process gas fromthe process space 3, via the second feed/discharge line 12.

[0060] When the inventive method is carried out, first the valve 8 isopened by the regulating unit 9 and process gas is conveyed into theprocess space 3 by the pump 11. Furthermore, valve 13 is opened andprocess gas is extracted from the process space 3 by the pump 14. Theprocess gas flows through the first feed/discharge line 7 into theprocess space 3. The process gas rises laterally upward past the boat 4,and a main flow direction 15 is formed. From the process gas flowascending along the main flow direction 15, portions diffuse away to theside into the interspaces between the wafers of the boat 4 that arearranged one above the other. In this case, the process gas flow iscontinuously depleted of the components that are deposited on thesurface of the wafers, so that a concentration gradient is formed alongthe main flow direction 15. Finally, the process gas flow leaves theprocess space 3 through the second feed/discharge line 12 and isextracted using the pump 14. After a specific time period has elapsed,under the regulation of the regulating unit 9, the valves 8, 13 areclosed and the pumps 11, 14 are stopped. The pumps 11, 14 are thenswitched such that the pump 14 conveys process gas into the processspace 3, while the pump 11 extracts process gas from the process space3. After the valves 8, 13 have been opened, the process gas then flowsfrom above into the process space 3, so that the main flow direction 15is reversed. As a consequence, a concentration gradient running in theopposite direction is formed, i.e. the greatest layer thickness growthis now observed at the upper end of the boat 4, where initially theleast layer thickness growth took place. As a result, it is possible tocompensate for differences in the layer thickness growth betweenindividual wafers of the boat 4, so that within a batch, thefluctuations in the layer thickness can be considerably reduced.

[0061] A measuring unit 17 can detect a quantity and/or a distributionof the components deposited onto the semiconductor substrate 6. Acontrol unit 18 is connected to the measuring unit 17. The control unit18 is for an online control of the pumps 11, 14.

[0062] FIGS. 2A-2D diagrammatically show various steps performed in oneembodiment of the inventive method. The arrangement of the first andsecond feed/discharge lines 7, 12 in the furnace 1 illustrated in FIGS.2A-2D differs from that shown in the furnace 1 illustrated in FIG. 1. Inthe furnace 1 illustrated in FIGS. 2A-2D, the process gas flow isdeflected at the upper end of a partition 2 and then guided downwardlaterally at the partition 2. As a result, the connections for the firstand second feed/discharge lines 7, 12 can all be arranged at theunderside of the furnace 1. The valves and the regulating unit forcontrolling the process gas flow are not illustrated for the sake ofclarity. In the first method step, as illustrated in FIG. 2A, processgas is introduced into the process space 3 via the first feed/dischargeline 7, rises upward past the boat 4 and is deflected at the upper endof the partition 2 in order then to be guided downward and finally ledaway via the second feed/discharge line 12. After a specific time periodhas elapsed, the supply of the process gas is interrupted while theprocess gas, as shown in FIG. 2B, continues to be pumped away from theprocess space 3 via the second feed/discharge line 12. Process gasesstill present in the process space 3 are therefore essentially removed.As an alternative, the process space 3 can also be flushed with an inertgas. Finally, as illustrated in FIG. 2C, the process gas is introducedinto the process space 3 through the second feed/discharge line 12 andis discharged from the process space 3 through the first feed/dischargeline 7, so that the main flow direction is reversed in the process space3. After a specific time period has elapsed, the supply of the processgas is interrupted again while the process gas, as shown in FIG. 2D,continues to be extracted from the process space 3 via the firstfeed/discharge line 7. After spent process gases have been extractedagain, as illustrated in FIG. 2D, the cycle illustrated in FIGS. 2A-Dcan be carried out again, if appropriate.

[0063]FIG. 3 diagrammatically shows the distribution of the layerthickness produced during the individual process stages of the method.In this case, the ordinal number of the wafer 6 within the stack isspecified on the X axis. The wafer 1 is arranged at the lower end inFIG. 1, while the wafers with higher numbers are arrangedcorrespondingly further up in the boat 4. The layer thickness growth isspecified on the Y axis. If the process gas is introduced into theprocess space 3 through the first feed/discharge line 7 and passed outof the process space through the second feed/discharge line 12, then ahigher layer thickness growth takes place on wafers with a low ordinalnumber than on wafers with a high ordinal number since the former arearranged nearer to the first feed/discharge line 7, and the process gasflow has a high concentration of the component to be deposited. If thelayer thickness growth is measured, then curve “A” illustrated in FIG. 3is obtained. After reversing the flow direction, the process gas thenflows into the process space through the second feed/discharge line 12and is passed out again via the first feed/discharge line 7. The waferswith a high ordinal number then correspondingly experience a morepronounced layer thickness growth than the wafers with a low ordinalnumber. If the layer thickness growth is measured, curve “B” illustratedin FIG. 3 is correspondingly obtained. Since the two curves “A” and “B”are ultimately added, curve “C” is obtained after carrying out themethod.

[0064]FIG. 4 shows the distribution of the layer thickness when carryingout a prior art method for depositing a layer on a wafer. The sameapparatus as illustrated in FIG. 1 is used, but the main flow directionis not varied. Therefore, during the entire deposition, the process gasis introduced into the process space 3 at the feed line 7 and, after ithas flowed through the process space 3 along a main flow direction 15,the process gas is discharged from the process space 3 at the dischargeline 12. As described above, a concentration gradient is establishedalong the main flow direction 15 and leads to a different layerthickness growth on the wafers 6 arranged in the process space 3. Wafers6 that are arranged nearer to the feed line 7 experience a higher layerthickness growth than wafers 6 that are arranged nearer to the dischargeline 12. The distribution of the layer thickness is illustrated in FIG.4. In this case, as in FIG. 3, the wafer number is plotted on theabscissa and the layer thickness is plotted on the ordinate. A curve “D”is obtained, which essentially corresponds to the curve A from FIG. 3.If the layer thicknesses of the wafers 6 are compared after the end ofthe layer deposition, curve “C” from FIG. 3 exhibits significantlysmaller deviations in the layer thickness in comparison with curve “D”shown in FIG. 4.

I claim:
 1. A method for vapor phase deposition, which comprises: vaporphase depositing components contained in a process gas flowing along amain flow direction onto at least one semiconductor substrate situatedin a process space; and during the step of vapor phase depositing,changing the main flow direction at least once.
 2. The method accordingto claim 1, wherein the step of changing the main flow direction isperformed by reversing the main flow direction.
 3. The method accordingto claim 1, which further comprises: orienting the main flow directionparallel to an axis of symmetry of a plurality of semiconductorsubstrates in the process space.
 4. The method according to claim 3,wherein the axis of symmetry is a rotation axis or a rotary mirror axis.5. The method according to claim 1, which further comprises: at leastpartially removing the process gas from the process space beforeperforming the step of changing the main flow direction.
 6. The methodaccording to claim 5, wherein the step of at least partially removingthe process gas is achieved by performing at least one step selectedfrom a group consisting of reducing a supply of the process gas into theprocess space, extracting the process gas from the process space, andflushing the process space with an inert gas.
 7. The method according toclaim 1, which further comprises: after performing the step of changingthe main flow direction, providing the components with a differentcomposition and/or a different concentration in relation to beforeperforming the step of changing the main flow direction.
 8. The methodaccording to claim 1, wherein the components react chemically with thesemiconductor substrate.
 9. The method according to claim 1, whichfurther comprises: performing the step of vapor phase depositing belowatmospheric pressure.
 10. The method according to claim 1, wherein thestep of changing the main flow direction is performed in accordance witha variable time pattern.
 11. The method according to claim 1, whichfurther comprises: while performing the step of vapor phase depositing,detecting a quantity and/or a distribution of the components beingdeposited onto the semiconductor substrate.
 12. The method according toclaim 1, which further comprises: while performing the step of vaporphase depositing, detecting a quantity and/or a distribution of thecomponents being deposited onto the semiconductor substrate whileonline.
 13. A furnace for vapor phase depositing components contained ina process gas onto at least one semiconductor substrate, the furnacecomprising: a process space for receiving the semiconductor substrate; afirst feed/discharge line connected to said process space; a secondfeed/discharge line connected to said process space; a device forproducing a process gas flow, said device for producing said process gasflow connected to said first feed/discharge line and/or said secondfeed/discharge line; a heating device; and a regulating unit forregulating a magnitude and a flow direction of said process gas flow.14. The furnace according to claim 13, wherein said first feed/dischargeline and/or said second feed/discharge line are configured at oppositesides of said process space.
 15. The furnace according to claim 13,wherein said regulating unit is configured for changing a main flowdirection of said process gas flow at intervals in accordance with avariable time pattern.
 16. The furnace according to claim 13, furthercomprising: a measuring unit for detecting a quantity and/or adistribution of the components deposited onto the semiconductorsubstrate.
 17. The furnace according to claim 16, further comprising: acontrol unit connected to said measuring unit, said control unit for anonline control of said device for producing a process gas flow.